1. Field of the Invention
The present invention relates to grapple skidder suited for moving an elongated load, such as a group of trees or logs, from one location to a selected location on a terrain.
2. Description of the Prior Art
It is well known to use grapple skidders to drag loads of logs from one location to a selected site. Conventional grapple skidders typically comprise a grapple suspended at the free distal end of a boom mounted on a tow vehicle. The grapple is usually hydraulically operated to open and close about one end of the load to be skidded. In the open position, the grapple is lowered to surround the butt end portion of a load of logs. Then, the grapple is closed and lifted to a position where the grasped end of the load of logs abut the rear end portion of the vehicle rearwardly of the rear axle thereof. This causes substantial tipping forces on the boom section tending to pivot the same rearwardly.
To minimize such tipping forces, it has been proposed, as exemplified by U.S. Pat. No. 3,782,567 issued on Jan. 1, 1974 to Likas et al., to use a boom assembly comprising a small linear boom arm pivotally mounted at a distal end of a main C-shaped boom which is, in turn, pivotally mounted to a vehicle.
Although the structure of the boom assembly disclosed in the above mentioned patent allows to drag an elongated load with one end thereof elevated over the rear axle of the vehicle so as to reduce the couple exerted on the boom by the dragged load, it has been found that there is a need for a new grapple skidder having a boom and grapple assembly offering increased freedom of movement.
It has also been found that there is a need for a grapple skidder having a boom and grapple assembly which can be operated to stack a bundle of trees or logs over another bundle of trees or logs lying on a ground surface.
It is therefore an aim of the present invention to provide a new grapple skidder having a boom and grapple assembly adapted to lift an elongated load over a ground surface.
It is also an aim of the present invention to provide a grapple skidder which offers increased freedom of movement.
It is a further aim of the present invention to provide a method for completely elevating an elongated load over a ground surface with a grapple skidder.
Therefore, in accordance with the present invention, there is provided a grapple skidder comprising a vehicle, a boom mounted to a rearward end portion of the vehicle, a grapple articulately suspended from a distal end of the boom for grasping an elongated load, and a heel mounted to the boom at a spaced location from the grapple for providing an arresting surface for the elongated load. The boom is pivotable to a first position to locate the grapple beyond the vehicle for embracing the elongated load at a location comprised between a leading end and the center of gravity thereof, and to a second position for lifting the leading end of the elongated load above a ground surface against the arresting surface to retain the elongated load against pivotal movement due to gravitational forces, whereby further pivotal movement of the boom from the second position thereof in a direction away from the first position results in the elongated load being completely lifted above the ground surface.
In accordance with a further general aspect of the present invention, there is provided a grapple skidder comprising a vehicle, a boom mounted to a rearward end portion of the vehicle, a grapple suspended from a distal end of the boom for grasping an elongated load, and a heel mounted to the boom for providing an arresting surface for the elongated load. The boom is pivotable from a first position to locate the grapple beyond the vehicle for embracing the elongated load at a location comprised between a leading end and the center of gravity thereof, to a second position in which the elongated load is completely lifted above a ground surface with the leading end thereof abutting against the arresting surface of the heel, thereby precluding pivotal movement of the grapple and the elongated load relative to the boom due to gravitational forces acting on the elongated load at the center of gravity thereof.
In accordance with a further general aspect of the present invention, there is provided a method of lifting an elongated load over a ground surface with a grapple skidder having an arresting surface, comprising the steps of:
a) grasping the elongated load with a grapple at a selected location comprised between a first end of the elongated load and a center of gravity thereof,
b) lifting the first end of the elongated load above the ground surface against the arresting surface of the grapple skidder so as to retain the elongated load against pivotal movement due to gravitational forces, and
c) applying further lifting forces at the selected location to completely elevate the elongated load above the ground surface.
In accordance with a further general aspect of the present invention there is provided a grapple skidder comprising a boom assembly including a linear main boom and an arched boom arm. The main boom is mounted to a vehicle for pivotal movement with respect thereto about a substantially horizontal axis. The arched boom arm is pivotally mounted to the main boom. A grapple is mounted at a distal end of the arched boom arm for grasping one end portion of an elongated load to be dragged. At least one arm cylinder extends between the main boom and the arched boom arm for pivoting the same relative to the main boom. The main boom is pivotable relative to the vehicle between first and second positions, wherein in the first position, the main boom is inclined forwardly with respect to a direction of travel of the vehicle during skidding, thereby allowing the elongated load to be dragged with one end portion thereof lifted over the rearward end of the vehicle, while minimizing the overall dimensions of the boom assembly when not in use.